The use of strobe lights to observe objects in motion is well known. The strobe flash enables the human eye to observe action which is occurring at high speed as though the action had stopped or is occurring in slow motion. Perhaps the best known use of the strobe principle is in the adjustment of the timing sequence in an automotive engine in relation to the action of the camshaft.
There are many applications in which it is desirable to observe motion inside an enclosed cavity. Examples of such applications are turbine blades inside a gas turbine engine or valve motion within the cylinders of a reciprocating engine. Such applications require remote visual inspection utilizing a borescope, a flexible fiberscope or a videoscope with a flexible light guide. These instruments use a light guide to transmit light from an external light source through the instrument to illuminate the internal area to be inspected. Such instruments enable an operator to visually inspect internal surfaces of objects which an operator cannot see without disassembling or cutting apart the object.
Prior art systems for remote visual inspection include stroboscopic light sources ("light sources") which have included features such as automatic synchronization of the flash rate of the strobe to the rate of rotation of the object being observed ("target object") and the use of a time delay to delay the firing of the flash to allow an operator to observe the moving object at a fixed time increment after a trigger signal is received. Since the position of the flash in a cycle will change as the speed of the moving object changes, it is imperative that the motion of the object being observed remains constant. Such prior art light sources do not provide an operator access to the flash to adjust the focus of the flash each time the light source requires maintenance.
The prior art light sources have generally been either large units or comprise a number of modules that are not amenable to use in the field. The light sources have been developed to accommodate inspection in a specific location and are not intended to be lightweight and portable.
Interference problems arise when attempting to house a stroboscopic light source including control electronics and a flash unit in a single housing. The interference causes the control electronics to produce false trigger signals to the flash unit thereby causing the flash unit to constantly fire.
The interference that results when attempting to house a light source in a single housing is caused by the large release of energy that occurs each time the flash unit is fired. In a typical prior art stroboscopic light source, a Xenon gas discharge lamp is used to produce a high intensity light pulse of short duration that is needed for stroboscopic illumination. The lamp operates on the principal that Xenon gas is not conducting electricity until it is ionized. Electrical energy is stored in a capacitor connected to the flash lamp to ionize the gas.
Upon receiving a flash trigger signal from the control electronics indicating that the flash lamp should be fired, a high voltage spike (approximately 10,000 volts) ionizes the Xenon gas in the bulb. When the gas in the lamp conducts, the electrical energy stored in the capacitor will rapidly discharge through the Xenon gas thereby causing the lamp to flash.
Based upon typical values of 650 volts and 10 microfarads for the energy storing capacitor, and a flash duration of 2 microseconds, the energy stored in the capacitor is calculated to be 2.1 VAsec (joules) by substituting the foregoing capacitor characteristics into the equation below where E represents energy, V represents voltage and C represents capacitance. EQU E=1/2V.sup.2 C
The power dissipated by the discharging of the capacitor is calculated by the following equation to be one megawatt. EQU Power=Energy/Time=2.1 VAsec/2 microseconds=1 megawatt
Furthermore, the current that travels through the circuit coupled to the capacitor as the capacitor discharges is calculated to be 3,250 amperes.
This large release of energy occurs in pulses. These pulses of rather large magnitude with sharp rise and fall times cause severe electromagnetic interference ("EMI"). As a result, any piece of material, i.e., wires, copper on printed circuit boards, etc., that are in the path of the EMI will act as receiving antennas for the EMI generated. The result is that false signals are generated which cause the associated control electronics to malfunction.
The foregoing problems of prior art light sources manifest the need for improvement. Specifically, there is a need for system employing a stroboscopic light source which houses the flash lamp and the control electronics in the same housing, allows for accurate observation of a specific point on an object being observed and provides an operator with the ability to focus the flash lamp.